A Global Study of the Behaviour of Black Hole X-ray Binary Discs

TL;DR

This study analyzes black hole X-ray binary accretion disc behavior during outbursts, confirming the near-constant disc radius and color correction in disc-dominated states and exploring deviations related to system parameters and black hole spin.

Contribution

It provides a comprehensive analysis of disc luminosity-temperature relations and constraints on system distances, masses, and black hole spin in low-mass black-hole X-ray binaries.

Findings

Disc luminosity follows L ~ T^4 in most disc-dominated states.

Deviations from T^4 law occur at state transitions, likely due to changes in f_col.

Distances and masses suggest some black holes may be spinning.

Abstract

We investigate the behaviour of the accretion discs in the outbursts of the low-mass black-hole X-ray binaries (BHXRB), an overview of which we have presented previously. Almost all of the systems in which there are sufficient observations in the most disc dominated states show a variation of the disc luminosity with temperature close to L ~\propto T^4. This in turn implies that in these states, the disc radius, R_in, and the colour correction factor, f_col, are almost constant. Deviations away from the T^4 law are observed at the beginning and end of the most disc dominated states, during the intermediate states. Although these could be explained by an inward motion of the accretion disc, they are more likely to be the result of an increase in the value of f_col as the disc fraction decreases. By comparing the expected and observed disc luminosities, we place approximate limits on the allowed distances and masses of the BHXRB system. In a number of cases, the measured distances and masses of the BHXRB system indicate that it is possible that the black hole may be spinning.